The present invention relates generally to oil well sucker rods and particularly to threaded sucker rod couplings which are threadedly secured to one another to form a string of rods and to a method of refurbishing the threaded end portions of used sucker rods.
Oil well sucker rods are threadedly secured to one another to form a string which runs from a pumping jack at the top of the well bore to a reciprocating pump set at a desired location in the well bore. An intermittent loading is placed upon the sucker rods during operation of the well as the rods in the string are loaded upon their upward movement as a result of the pump load and the fluid column above the pump. The weight of the chain of rods and the alternating motion of the pumping operation sets up severe repetitive stresses in the sucker rod chain. As a result, the sucker rod chain is fatigued and premature failure often occurs at the threaded couplings. In the past, the procedure employed has been to inspect the sucker rod chain at approximate six month intervals with the faulty sucker rods being discarded and sold as scrap.
Various types of couplings for sucker rods have previously been suggested to overcome the problem of failure in the threaded connections. U.S. Pat. No. 1,064,764 to Parker, issued June 17, 1913, shows a coupling for use with uniform diameter sucker rods which utilizes a cylindrical sleeve to join successive rods. U.S. Pat. No. 1,538,093 to Dale, issued May 19, 1925, shows a coupling used with a sleeve and having feathered edges which are crimped down in forming the connection. U.S. Pat. No. 2,874,937 to Higgins, issued Feb. 24, 1959, shows a coupling which is attached to a cylindrical fiberglass rod by driving a tapered tool into the end of the rod to expand it. A cylindrical sleeve is used to join the pin ends of successive rods. U.S. Pat. No. 3,489,445 to Kammerer, Jr., issued Jan. 13, 1970, shows a prestressed joint which utilizes an elastomeric washer and which utilizes a cylindrical sleeve to couple the pin ends of successive rods.
In each of these references, the resulting sucker rod joint has a pin end which is joined by means of a cylindrical sleeve to the pin end of the next successive rod. The result is two separate connecting points and, thus, two potential weak spots in the sucker rod chain for each coupling. In addition, although the above references suggest various couplings which are intended to lessen the possibility of failure in the threaded ends, no method is suggested for refurbishing a used sucker rod having damaged threaded ends. Rather, damaged sucker rods have generally been discarded at great expense.
There exists a need, therefore, for a sucker rod having improved coupling capabilities which will reduce the instance of failures in the threaded connections. There also exists a need for a refurbishing method for use on damaged rods which will allow damaged rods to be reused.